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updated 11/4/2011 12:19:59 PM ET 2011-11-04T16:19:59

You don't have to swim in polluted waters to get sick from floating microorganisms, found a new study. Simply canoeing or rowing on the surface may be enough to slightly increase your risk of intestinal distress.

The study was the first to look at the health consequences of boating on contaminated bodies of water. And while the risks were not enormous or life threatening, the findings suggest that better pollution regulation and warning systems could prevent a significant number of illnesses.

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Boaters, too, might want to consider bacterial hazards when they choose to go out on certain lakes or rivers.

“There are waters where swimming is prohibited but boating and other water activities are permitted, and the water can be pretty dirty,” said Sam Dorevitch, an environmental physician at the University of Illinois School of Public Health in Chicago. “If the water has a lot of bacteria or viruses in it and people get a splash, that might be all it takes to make them sick.”


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Tens of millions Americans take part in rowing, canoeing, kayaking, fishing or motor-boating each year. Under the assumption that boating is safe, even when the water is dirty -- the Clean Water Act allows these kinds of activities in many places that are deemed too polluted for swimming.

To find out what the true risks are, Dorevitch and colleagues recruited more than 11,000 people in the Chicago area over the course of three summers. About a third of participants partook in boating activities on the Chicago River, which consists primarily of non-disinfected wastewater discharge. A third recreated on inland lakes, rivers, or Lake Michigan beaches that were approved for swimming. The final third did terrestrial activities, such as cycling or running, in the same areas around the same times of year.

Afterwards, the researchers asked participants all sorts of questions about how much contact they’d had with the water and whether any water had ended up in their mouths. Over the next three weeks, each person answered three rounds of questions about any symptoms that had arisen.

Groups who boated on both polluted and clean waters had a one to two percent higher risk of developing diarrhea, nausea or vomiting compared to the group that stayed on dry land, the researchers reported in the journal Environmental Health Perspectives. That added up to an extra 15 or so cases of gastrointestinal issues per thousand people who did aquatic activities.

The reason the numbers were similar for the two water groups, the researchers speculate, is that people reported submerging their heads in the clean water much more often, and they likely swallowed significantly more water. So, even though the contaminated water had far more bacteria in it, both groups probably ended up with similar levels of exposure to microorganisms.

For people who boated on dirty water, the study also found a one percent higher risk of developing eye problems compared to the other two groups – with an extra 10 cases of itchy, irritated or crusty eyes per thousand people. The more contact with water people had during their activities, the more likely they were to end up with eye, ear, breathing or GI symptoms.

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None of the illnesses the study recorded were severe or long-term, Dorevitch said, and everyone got better with over-the-counter drugs or less. Still, the findings should allow people to make more educated decisions about how much extra risk they’re willing to accept for themselves or for their kids.

"Essentially what they're saying," said Steve Weisberg, executive director of the Southern California Coastal Water Research Project in Costa Mesa, "is that there's enough contact from people just getting their hands wet from splashes and putting their hands in their mouths that there is an increased risk of illness."

As policy-makers decide whether the new results warrant revised warning systems, boaters can protect themselves by investigating the cleanliness of their local lakes, rivers and ocean beaches.

"This country has some of the best beach monitoring programs in the world," Weisberg said. "If you have doubts, check with your local health department because they are probably monitoring beaches and will tell you which is safest.”

© 2012 Discovery Channel

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